Institute of Astronomy

MHD turbulence and state changes in compact X-ray sources

SpeakerTalk DateTalk Series
Steve Balbus (Oxford)6 February 2014Institute of Astronomy Colloquia



There is evidence that the saturation levels of MHD turbulence are
sensitive to the ratio of the small scale viscosity to resistivity,
a quantity known as the magnetic Prandtl number Pm. This sensitivity is present when Pm ~ 1.

Interestingly, discs associated with compact X-ray sources have such a low-to-high (tracking inward) Pm transition radius on scales of tens of Schwarzschild radii. These disc sources are also known for their dramatic changes in their spectral states.

In this talk, I will show that standard alpha disc theory predicts Dwarf-Nova like outbursts when the turbulent stress is even a modestly increasing function of Pm. Implications for understanding the X-ray data will be presented, both successes of the theory and remaining challenges.


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